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Full text of "Text Book Of Mechanical Engineering"

Geared Punching and Shearing Machine.         289

tageous. Mr. Tweddell advocated the almost universal appli-
cation of hydraulics for plate work, and fully confirmed his advo-
cacy of the system, especially where the power had to1 be taken
about to various places in succession. In all shops Riveting
Machines and Flanging Presses are now actuated by water
pressure; so also may be Punching and Shearing Machines,
though more often driven by shafting; while Drilling, usually
performed by shaft power, has been successfully attacked by
electricity and water pressure; portable hydraulic drills, under
certain conditions, having proved both efficient and economical.

Punching and Shearing Machines.—It is customary
to combine both operations in one machine, as a plate is seldom
punched and sheared at the same time. Fig. 283 shews a good
example of this tool, as made by Mr. John Cochrane, of
Barrhead, capable of either punching, shearing, or angle cutting.
A shaft A has fast and loose pullies at B, and fly wheel at c for
overcoming variable resistance. The power passes, by pinion
and wheel, D and E, to a second motion shaft F, and in like
manner, by wheels G and H, to the main shaft j. The shaft j
has eccentric pins KK formed upon its ends to give a vertical
reciprocating motion to the slides L and M, the former carrying
the punch, and the latter the shearing knife. Dies upon the
pins KK prevent undue wear, and the fork N prevents the rising
of the plate when the punch is withdrawn. The shearing knife
always moves while the driving shafts revolve; but the punching
slide L is driven from pin K through the hollow die P and a
cam piece Q, the latter being connected to a handle R. When
R is upright the downward motion of P is transferred to L: but
if the handle be laid on its side, so also is the cam; P then
moves freely without pressing upon L, and no punching occurs.
Thus by changing position of R, the workman has ample time to
set his plate, while the shafts still revolve. The dies are hard
steel, and steel plates in slide M receive the wear. The angle-
shearing knife is fastened to a rocking lever s, actuated frotn
shaft j by an eccentric T, having ball and socket connection to
the lever* Here, again, the withdrawal of a sliding piece t; serves
to stop the motion of the knife, which is necessary with hars,
though not vrith plates.